Thermal shock triggers microexplosion combustion in graded fuel and oxidizer encapsulation microspheres with improved combustion efficiency

• Published in: Combustion and flame 2024-07, Vol.265, p.113499, Article 113499
• Main Authors: Zhang, Hong-Yu, Shi, Zhe, Dong, Ya-Yu, Wang, Xu-Wen, Lin, Kai-Feng, Xia, De-Bin, Zhang, Jian, Yang, Yu-Lin
• Format: Article
• Language: English
• Subjects: Energetic material; Graded fuel and oxidizer encapsulation; Microexplosion combustion; Solid propellant; Thermal shock
• ISSN: 0010-2180
• DOI: 10.1016/j.combustflame.2024.113499

•Graded fuel and oxidizer integrated microspheres improve combustion performance.•Thermal shock induces local cavitation effect leading to microexplosive combustion.•Integrate the three-step thermal decomposition process of AP into a single step.•The reduced heat and mass transfer distance promotes energy release efficiency. The combustion agglomeration of aluminum (Al) and the long heat and mass transfer distance between Al and oxidizer cause serious two-phase flow loss and slag accumulation in the engine of solid propellants. Here, we present an effective strategy by in-situ encapsulating graded nano-aluminum (nAl) and micron-aluminum (μAl) in ammonium perchlorate (AP) simultaneously by using hydroxymethyl cellulose (HMC) as adhesive and constructing a compact coupling fuel oxidizer complex high-energy microsphere (μAl/nAl@AP/HMC) to enhance the energy release efficiency and combustion efficiency. Compared with physical mixture (PM), the ignition delay time and combustion time of μAl/nAl@AP/HMC microspheres are reduced by 69.58 % and 69.87 %, owing to the decomposition process control of AP through the adsorption and spatial constraint effect on the interface between metal fuels and oxidizer. Furthermore, the nAl embedded in the AP surface forms a hot spot around the μAl to promote the combustion reaction, thereby shortening the cavitation threshold and tensile limit time of μAl and accelerating the occurrence of microexplosion. Microexplosion effect in μAl/nAl@AP/HMC microsphere significantly weakens combustion agglomeration and improves combustion efficiency and energy release efficiency by sharp shrinkage of combustion condensation products, which addresses the challenges on energy output and combustion efficiency in high-density solid propellants. The composite energetic microspheres (nAl/μAl@AP/HMC) were prepared using a self-assembly method, where graded fuels(nAl and μAl) were encapsulated within an oxidizer, ammonium perchlorate (AP). High reactive nAl produces thermal shock during combustion, which effects local cavitation effect on the μAl, and then triggers microexplosive combustion of microspheres. The adsorption effect of graded nAl on the gaseous products of AP decomposition modifies the three-step decomposition process of AP into a single-step decomposition, resulting in facilitating the concentrated release of acid and oxidizing gases during AP decomposition. [Display omitted]